1. Field of the Invention
The present invention relates to a multilayer printed wiring board provided with a power supply layer having a plurality of power supply patterns with different power supply voltages.
2. Description of the Related Art
A conventional multilayer printed wiring board generally has a structure including at least one signal layer, at least one power supply layer, and at least one ground layer. Since power supply voltage used in a power supply layer in electronic equipment having a conventional digital circuit is mainly 5 V, a single 5 V power supply pattern is formed in the power supply layer in many cases.
In a conventional printed circuit board, a connector to which power is supplied is arranged in proximity to an LSI (large scale integration) the power consumption of which is highest on the board. Further, a power supply pattern formed from the power supply connector to an area where the LSI with the highest power consumption is mounted is made the thickest, and power supply patterns to ICs (integrated circuits) including other LSIs are made thinner according to the amount of electric current. This makes the power supply voltage supplied to the LSI with the highest power consumption and the power supply voltage supplied to an LSI which transmits and receives a signal to and from the LSI with the highest power consumption substantially equal on the circuit board (see, for example, JP 2002-374048 A).
However, since voltages supplied to and power consumptions of ICs are required to be reduced in recent years, 5 V power supply voltage and 3.3 V power supply voltage or lower are supplied to ICs in many cases.
As a result, the power supply layer is not formed of a single 5 V power supply pattern. For example, two power supply patterns of 5 V and 3.3 V or more than two power supply patterns insulated from each other are formed on the power supply layer.
In the conventional multilayer printed wiring board, since a plurality of power supply patterns with different power supply voltages exist on one power supply layer, when, for example, a 3.3 V power supply pattern for supplying power to a 3.3 V power supply pin of an IC is formed after a 5 V power supply pattern for supplying power to a 5 V power supply pin of the IC is formed, it is necessary to detour the already formed 5 V power supply pattern. Therefore, there is a problem in that the 3.3 V power supply pattern is lengthened, the impedance is increased, and thus, electromagnetic radiation noise radiated from the power supply pattern is increased.